Methods

Six female AGMs and four female RMs were hormonally-induced into lactation prior to intravenous inoculation with SIVsab92018 and SIVmac251, respectively. B cells in milk and blood were phenotypically analyzed by flow cytometry. Total and SIV gp120-specific IgG/IgA responses in milk and plasma were measured using autologous virus-specific ELISA.

Results

SIV gp120-specific IgG responses were approximately one log higher in milk (p=0.02) and plasma (p=0.009) of AGMs compared to that of RMs. Remarkably, the milk SIV gp120-specific IgA response of AGMs was two logs higher than that of RMs (p=0.009). Comparing the milk SIV gp120-specific IgA responses to other mucosal compartments of AGMs, milk responses were higher than rectal (p = 0.03), but similar to vaginal responses. Although there were no significant differences in the milk memory B cells populations of AGMs and RMs, we observed a reduced proportion and absolute number of naive B cells (CD20+, IgD+, CD27-) in milk of RMs (median = 7.9%, 0.16 cells/µl) compared to AGMs (median = 26.5%, 4.2 cells/µl) (p = 0.009 and 0.06, respectively) during chronic infection.

Conclusion

AGMs appear to preserve SIV-specific IgG/IgA responses in milk during chronic infection, potentially due to a lack of immune activation and B cell dysfunction, which may contribute to the rarity of postnatal SIV transmission in this natural host species.

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Corresponding author

Correspondence to
JD Amos.

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This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.